1. Field of the Invention
The present invention relates to an ink suited for an ink-jet printer, an ink-jet device making use of it and an ink cartridge containing the ink. It also relates to an ink-jet recording process that makes a record on non-coated paper, called plain paper, by causing ink to fly from orifices of a recording head by the action of heat energy.
2. Related Background Art
Ink-jet recording systems have the advantages that they make less noise in the course of recording and a recorded image with a high resolution can be obtained at a high speed because of use of a highly integrated head. Inks used in such ink-jet recording systems are those prepared by dissolving various kinds of water-soluble dyes in water or in a mixed solution of water and an organic solvent. When the water-soluble dyes are used, however, light fastness of recorded images is often questioned because such water-soluble dyes have poor light fastness by nature.
Water resistance of recorded images is also often questioned because the ink is water-soluble. More specifically, if recorded images become wet with rain, sweat, or water from food and drink, they may become blurred or disappeared.
Meanwhile, similar questions have arisen also with respect to writing implements such as ball-point pens making use of dyes, and various water-based pigment inks for writing materials have been proposed so that the problems of light fastness and water resistance can be settled. Examples of studies on dispersion stability, prevention of ink solidification at pen points and prevention of ball wear of ball-point pens for the purpose of putting water-based pigment inks into practical use are seen in Japanese Patent Applications Laid-open No. 58-80368, No. 61-200182, No. 61-247774, No. 61-272278, No. 62-568, No. 62-101671, No. 62-101672, No. 1-249869, No. 1-301760, etc. Recently, ball-point pens or markers making use of water-based pigment inks have become commercially available.
When, however, conventional water-based pigment inks for writing implements are applied in an ink-jet recording apparatus of the system that makes a record by causing ink to fly from orifices of a recording head by the action of heat energy, there have been disadvantages such that serious difficulties may arise in ejection stability, causing defective prints. In particular, in a system that makes a record by ejecting droplets by the action of heat energy applied, use of the conventional pigment ink may cause the formation of deposits on a thin-film resistor because of the heat generated when pulses are applied to the ink, so that the ink may be imperfectly bubbled and the ejection of droplets can not respond to the applied pulses, often resulting in no ejection of ink. Namely, in order for an ink to be stably ejected from nozzle tips, the ink must have the performances that it can be bubbled on a thin-film resistor to form bubbles with the desired volume and also it can be repeatedly bubbled and debubbled at the desired intervals. None of conventional inks for writing implements, however, have satisfied such performances, and hence various difficulties as stated above may occur when loaded in an ink-jet recording apparatus to carry out recording.
Moreover, although some conventional water-based pigment inks have a good performance when ejected for a relatively short time, but such inks experienced problems such that ejection becomes unstable when drive conditions of a recording head are changed or ink is continuously ejected over a long period of time, finally resulting in no ejection.
As a water-based pigment ink that can be preferably used in the above ink-jet recording, EP 0376284 A2 discloses an ink characterized by having a superior ejection performance in ink-jet printers, response to variations of their drive conditions, stability in continuous ejection for a long period of time and restoration performance at the time of reprint after temporary stop of printing, and being particularly suited for ink-jet printers making use of heat energy. This ink, however, is required to be more improved in its anti-sedimentation during long-term storage of ink, the stability in ink properties, and the response to higher-speed drive.